SpeedFan is a freeware program that monitors voltages, fan speeds and temperatures in computers with hardware monitor chips. It can access S.M.A.R.T. info for those hard disks that support this feature and show hard disk temperatures too, if supported. SpeedFan can even change the FSB on some hardware.

At the lowest level, SpeedFan is an hardware monitor software that can access digital temperature sensors, but its main feature is that it can change fan speeds according to the temperatures inside your pc.